1. Field of the Invention
This invention relates to archery bow stabilizers for reducing vibrations of the bow to produce more accurate shooting.
2. Background
When an arrow is shot from an archery bow, the bow vibrates. The vibrational movement of the bow inhibits accuracy in shooting, causes physical discomfort to the shooter""s hand and arm, and causes wear and tear on the bow and string. A bow stabilizer device may be attached to the bow to dampen or absorb vibrational energy from the bow such that the bow motion is minimized.
As will be better understood by the following discussion, stabilizers essentially function as a shock absorber and provide inertial stability to the bow assembly. A shock absorber can be thought of as a combination of a damping element (or xe2x80x9cdamperxe2x80x9d) and a spring element. The spring captures energy from the bow and delivers it to the damper. The damper absorbs or dissipates energy delivered from the spring. The damper may also capture and absorb energy through its direct contact with the bow.
An oscillating system stores energy by vibrating at a characteristic resonance frequency. An oscillating system may also vibrate at harmonics of the resonance frequency, i.e., twice the resonance frequency, four times the resonance frequency, etc. The resonant frequency is proportionate to a constant commonly referred to as the spring constant or spring coefficient. The spring coefficient is a measurement of the stiffness of the system. Numerically, the spring coefficient is equal to the force required to produce a unit of change in length from the equilibrium position, and is generally expressed in Newtons per meter or pounds per foot. An oscillating system also has a damping factor associated therewith which dampens or diminishes the amplitude of the oscillations over time.
When an arrow is shot, the bow becomes an oscillating system, which, like other oscillating systems, has an inherent resonant frequency at which it vibrates. Likewise, archery bow stabilizers are oscillating systems with an inherent resonant frequency associated therewith. Stabilizers typically function in a manner analogous to a mass attached to a spring on a surface which has a damping factor caused by friction between the mass and the surface. The spring transfers motional energy to the mass, and the system oscillates. The mass acts as a damper because it dissipates energy due to friction between the mass and the surface.
In the same manner, bow stabilizers generally have a spring element and a damping element. Oscillations in the bow drive oscillations in the spring element of the stabilizer. The spring element transfers energy to the damping element, which has a damping factor associated therewith that is higher than the damping factor of the spring or bow for absorbing energy. Thus, bow stabilizers absorb or dissipate energy by transferring energy from the bow to the damper through a spring element. The damper/spring stabilizer system has an inherent resonant frequency which is referred to herein as a damping frequency.
An optimum amount of energy is absorbed when the inherent resonate frequency of the system being damped is equal to the damping frequency of the damper/spring shock absorber. This is commonly referred to as xe2x80x9ccritically damped.xe2x80x9d The damping frequency of a shock absorber that has a spring and a damper is proportional to the product of the spring coefficient associated with the spring and the spring coefficient associated with the damper.
Conventionally, there are three basic types of bow stabilizers. Each can be understood as a damper/spring shock absorber.
One type of bow stabilizer is a metal tube surrounding a damping fluid or gel. The metal tube functions as a spring of almost infinite stiffness, i.e., with an almost infinite spring coefficient. The fluid or gel is the damper and absorbs energy from the metal tube. The fluid or gel may also contain a piston that moves in the fluid to further dissipate energy. Because the xe2x80x9cspringxe2x80x9d in such a system has a nearly infinite spring coefficient, the natural frequency of the stabilizer is higher than the resonate frequency of the system being damped. Therefore, the system is underdamped.
Another type of bow stabilizer is an elastomeric element connected to a weight. In such a system, the elastomeric element functions as both a damper and a spring. Generally, the spring coefficient in this type of bow stabilizer is low, making the natural frequency of the stabilizer less than the natural frequency of the bow, and thus, the system is overdamped.
A third type of bow stabilizer is a rod and mass system. Rod and mass stabilizers use a system of movable weights to tune the stabilizer resonant frequency to that of the natural frequency of the system. The rods act as a spring to transfer the energy of the bow to the weights. The rods are fixed at both ends, and therefore, the frequency of the vibrations are proportional to the length of the rods and various harmonics thereof. The weights function both as a damper to absorb the energy and as a tuner. The weights may be moved to various positions along the rod. If the weight is placed at an antinode of a resonant frequency of the rod, a maximum amount of energy can be absorbed. This type of bow stabilizer most closely approximates the natural frequency of the system to attain critical damping. However, it is often difficult to tune the stabilizer for critical damping. In addition, because the weights must be moveable to tune the stabilizer, the size of the weight is limited. The damping factor is a function of the mass of the damping material. Thus, most tunable rod and mass configurations do not allow for enough damping material to adequately absorb the energy once it is captured by the stabilizer.
These and other problems are avoided and numerous advantages are provided by the apparatus described herein.
The present invention provides an archery bow stabilizer for damping bow vibrations. When a bow is shot, vibrations occur in the bow and string. These vibrations inhibit accuracy in shooting, cause discomfort in the hand and arm of the shooter, and causes wear and tear on the bow and string. The present invention dampens vibrations to increase accuracy in shooting, reduces shooter discomfort, and prolongs the lifetime of the bow and string. In addition, the present invention provides inertial stability to the bow and string assembly.
In an embodiment, the spring element is fixed at an end proximate to the bow, but is not fixed on its distal end. Because the spring element is not fixed at one end, it communicates vibrational energy in a range of frequencies to a damping element, and tuning is not required. The energy is dissipated by the damping element to minimize vibrations and motion in the bow. Because tuning is not required, the damping element is not movable and may extend the entire length of or even longer than the spring elements. Therefore, a larger damping element is provided for more efficiently damping bow motion.
In accordance with the invention, an archery bow stabilizer is disclosed. In an embodiment, an elongated damping element with a first and second end is connectable to an archery bow. A plurality of elongated linear spring rods is connected to the damping element at the first end, and a plurality of flutes connects the damping element to the rods.
When an archery bow is shot, it stores energy by vibrating at a characteristic resonance frequency. The vibrations of the bow are transferred to the elongated linear spring rods, which are configured to vibrate in a range of frequencies because they are fixed at only one end. The linear spring rods, which are in close contact with the damping element, transfer vibrational energy to the damping element where the energy is dissipated.
In another aspect of the invention, the stabilizer includes a base unit that is connectable to an archery bow. An elongated damping element which has a first and second end is connected to the base unit at its first end. A plurality of recessed flutes extends lengthwise along the damping element from the first end towards the second end. A plurality of elongated linear spring rods is connected to the base unit and parallel to the damping element. The rods are configured to fit within the recessed flutes.
Preferably, the damping element extends beyond the length of the rods. The stabilizer preferably includes one or more ribs that extend radially around the second end of the damping element. The stabilizer may also have an absorber mount for connecting the first end of the damping element to the base unit.
Preferably, the damping element is made from an elastomeric material, the rods are made from steel, and the base unit and absorber mount are made from aluminum. More preferably, the damping element is made from rubber.
Because the rods vibrate in a range of frequencies, it is not necessary to tune the stabilizer. The configuration of the damping element, which extends parallel to the spring elements, provides for a larger, more massive damping element for more efficient energy damping. Additional damping is provided by the portion of the damping element that extends beyond the length of the rods. Still more damping is provided by the ribs which extend radially around the second end of the damping element. These and other advantages will become apparent to those of ordinary skill in the art with reference to the detailed description and drawings.